Interleukin-17A (IL-17A also sometimes called IL-17) is the central lymphokine produced by a newly defined subset of inflammatory T cells, the Th17 cells. In several animal models, these cells are pivotal for various autoimmune and inflammatory processes. Increased levels of IL-17A have been associated with uveitis (Ambadi-Obi, et al 2007, Nature Med; 13:711-718), rheumatoid arthritis (RA), psoriasis, airway inflammation, chronic obstructive pulmonary disease (COPD), inflammatory bowel disease (Crohn's disease and ulcerative colitis), allograft rejection, cancer, intra-peritoneal abscesses and adhesions, and multiple sclerosis (Weaver, et al 2007, Annu Rev Immunol; 25:821-852; Witowski et al 2004, Cell Mol Life Sci; 61:567-579). Th17 cells can rapidly initiate an inflammatory response that is dominated by neutrophils (Miossec, et al 2009, NEJM; 361:888-98).
IL-17A was originally identified as a transcript from a rodent T-cell hybridoma. It is the founding member of a group of cytokines called the IL-17 family. Known as CTLA8 in rodents, IL-17A shows high homology to viral IL-17A encoded by an open reading frame of the T-lymphotropic rhadinovirus herpesvirus saimiri (Rouvier E, et al 1993, J. Immunol. 150: 5445-56).
IL-17A is a cytokine that acts as a potent mediator in delayed-type reactions by increasing chemokine production in various tissues to recruit monocytes and neutrophils to the site of inflammation, similar to interferon gamma. The IL-17 family functions in the role of proinflammatory cytokines that respond to the invasion of the immune system by extracellular pathogens and induces destruction of the pathogen's cellular matrix. IL-17A acts synergistically with tumor necrosis factor and interleukin-1 (Miossec P, et al 2009, N. Engl. J. Med. 361:888-98).
To elicit its functions, IL-17A binds to a type I cell surface receptor called IL-17R of which there are at least two variants, IL-17RA and IL-17RC (Pappu R, et al 2012, Trends Immunol.; 33:343-9). IL-17RA binds IL-17A, IL-17AF and IL-17F and is expressed in multiple tissues: vascular endothelial cells, peripheral T cells, B cell lineages, fibroblast, lung, myelomonocytic cells, and marrow stromal cells (Kolls J K, Lindén A 2004, Immunity 21:467-76; Kawaguchi M, et al 2004, J. Allergy Clin. Immunol. 114:1265-73; Moseley T A, et al 2003, Cytokine Growth Factor Rev. 14:155-74).
In addition to IL-17A, members of the IL-17 family include IL-17B, IL-17C, IL-17D, IL-17E (also called IL-25), and IL-17F. All members of the IL-17 family have a similar protein structure, with four highly conserved cysteine residues critical to their 3-dimensional shape. Phylogenetic analysis reveals that among IL-17 family members, the IL-17F isoforms 1 and 2 (ML-1) have the highest homology to IL-17A (sharing 55 and 40% amino acid identity to IL-17A respectively), followed by IL-17B (29%), IL-17D (25%), IL-17C (23%), and IL-17E being most distantly related to IL-17A (17%). These cytokines are all well conserved in mammals, with as much as 62-88% of amino acids conserved between the human and mouse homologs (Kolls J K, Lindén A 2004, Immunity 21:467-76).
IL-17A is a 155-amino acid protein that is a disulfide-linked, homodimeric, secreted glycoprotein with a molecular mass of 35 kDa (Kolls J K, Lindén A 2004, Immunity 21:467-76). The structure of IL-17A consists of a signal peptide followed by the amino acid region characteristic of the IL-17 family. An N-linked glycosylation site on the protein was first identified after purification of the protein revealed two bands in standard SDS-PAGE analysis, one at 15 kDa and another at 20 kDa. Comparison of different members of the IL-17 family revealed four conserved cysteines that form two disulfide bonds (Yao Z, et al 1995, J. Immunol. 155:5483-6). IL-17 is unique in that it bears no resemblance to other known interleukins. Furthermore, IL-17 bears no resemblance to any other known proteins or structural domains (Kolls J K, Lindén A2004, Immunity 21:467-76). Generally, other members of the IL-17 family such as IL-17F form homodimers (like IL-17A).
IL-17A is also known to form a heterodimer with IL-17F under certain circumstances. Heterodimeric IL-17AF is also produced by Th17 cells following stimulation by IL-23.
IL-17AF is thought to signal through the IL-17RA and IL-17RC receptors like IL-17A and IL-17F. The biological functions of IL-17AF are similar to those of IL-17A and IL-17F. Stimulation of target cells by IL-17AF induces the production of a variety of chemokines, in addition to airway neutrophilia in appropriate circumstances. IL-17AF is considered to be less potent in these activities than homodimeric IL-17A, but more potent than homodimeric IL-17F. For example, if the potency of IL-17A is 1, then the relative potency of IL-17AF is about 1/10 of that of IL-17A and the relative potency of IL-17F is about 1/100 of that of IL-17A. Human and mouse IL-17AF both show activity on mouse cells. IL-17AF consists of a total of 271 amino acids and has a molecular weight of approximately 30.7 kDa (data from product description of Human IL-17AF Heterodimer from Shenandoah Biotechnology).
A number of relevant crystal structures have been published. These include the crystal structure for homodimeric IL-17F (Hymowitz et al 2001, EMBO J, 19:5332-5341).
The crystal structure of IL-17F in complex with the receptor IL-17RA has also been published (Ely et al., 2009 Nature Immunology 10:1245-1251). In addition at least one crystal structure of IL-17A in complex with the Fab fragment of an antibody has been published (Gerhardt et al., 2009 Journal of Molecular Biology, 5:905-921).
Several inflammatory and autoimmune diseases including psoriasis are linked to exacerbated Th1 and/or Th17 responses. Many of them are currently treated either with general immunosuppressants or very selectively acting biologicals such as anti-TNF-α antibodies that are not effective in all patients. These were found to increase the risk for infections and to become ineffective after repeated treatment. Therefore, there is an unmet medical need for treatments with increased safety profiles and simultaneous capacity to induce long-term remission or cure of the disease.
Numerous immune regulatory functions have been reported for the IL-17 family of cytokines, it is presumed due to their induction of many immune signaling molecules. The most notable role of IL-17A is its involvement in inducing and mediating pro-inflammatory responses. IL-17A is also associated with allergic responses. IL-17 induces the production of many other cytokines (such as IL-6, G-CSF, GM-CSF, IL-1β, TGF-β, TNF-α), chemokines (including IL-8, GRO-α, and MCP-1), and prostaglandins (e.g., PGE2) from many cell types (fibroblasts, endothelial cells, epithelial cells, keratinocytes, and macrophages). The release of cytokines causes many functions, such as airway remodeling, a characteristic of IL-17A responses. The increased expression of chemokines attracts other cells including neutrophils but not eosinophils. IL-17 function is also essential to a subset of CD4+ T-cells called T helper 17 (Th17) cells. As a result of these roles, the IL-17 family has been linked to many immune/autoimmune related diseases including rheumatoid arthritis, asthma, lupus, allograft rejection and anti-tumor immunity (Aggarwal S, Gurney A L 2002, J. Leukoc. Biol. 71:1-8). Additionally, links have been drawn to further conditions such as osteoarthritis, septicemia, septic or endotoxic shock, allergic reactions, bone loss, psoriasis, ischemia, systemic sclerosis, fibrosis, and stroke.
Thus, there is a need for specific antibodies that antagonize the effects of IL-17A and are capable of inhibiting IL-17A induced activity, and especially compositions and methods of use for said antibodies to treat pathological disorders that can be treated by inhibition of IL-17A signaling.